The present invention relates to a closing module for an optical arrangement. The invention can be used in connection with the microlithography utilised in the manufacture of microelectronic circuits. It therefore also concerns a lens barrel which is suitable, in particular, for use in a microlithography device, and a microlithography device including such a lens barrel.
Lens barrels composed of a plurality of modules are used in a large number of optical applications, in particular in the field of microlithography mentioned above. The individual modules include, as a rule, one or more optical elements such as lenses, etc. The end of such a lens barrel in the direction of its optical axis is generally formed by a closing module having an appropriate optical closing element. Such a closing module may serve the purpose, among others, of sealing the interior of the lens barrel from the environment.
In particular in the field of microlithography it is necessary to position the optical elements used in the lens barrel, for example, the lenses, with the greatest possible spatial precision with respect to one another, in order to achieve appropriately high imaging quality. The high demands for accuracy are not least a result of the constant need to increase the resolution of the optical systems used in the manufacture of microelectronic circuits to drive forward the miniaturisation of the microelectronic circuits to be manufactured.
With increased resolution there are increasing demands not only for the positional accuracy of the optical elements used, but also for the accuracy of the optical elements themselves. The latter must be maintained as fully as possible in the installed state throughout operation. It is especially necessary to keep the optical element as free of stress as possible during operation to avoid imaging errors caused by deformation of the optical element. In addition, there is a need in this context to achieve the most favourable possible dynamic behaviour of the optical system used, with the highest possible resonant frequencies.
For the optical elements, i.e. the lenses, etc., inside the lens barrel a number of measures for achieving a mounting as stress-free as possible are known. For example, a comparatively complex and expensive mounting for such a lens inside the lens barrel is known from U.S. patent application Ser. No. 2002/1063741 A1. Patent DE 101 39 805 C1 and patent application EP 1 094 348 A2 also disclose variants for the mounting of lenses inside the lens barrel.
However, the above-mentioned closing elements present a problem in this context. They are in general mounted in a sealed manner in a corresponding mount, together with which they form the closing module. The closing elements, which are often plane-parallel plates, are often adhesively bonded to the mount. This type of fixing has the disadvantage, firstly, that it is not free of stress, so that deformations of the closing element which impair the imaging quality of the system can occur. Secondly—even with closing elements originally mounted in an almost stress-free manner—such undesired deformation can occur as a result of the unavoidable thermal expansion of the system in operation. Finally, subsequent adjustment of the closing element is, in particular, extremely difficult.
It is therefore the object of the present invention to make available a closing module of the type mentioned initially which does not have the above-mentioned disadvantages or at least has them to a lesser degree, and, in particular, makes possible a reliable mounting of the closing element which is precise and free of stress in operation.